Patent GB-1432045-A (GB)
Title: Pulse generating circuit for machining by intermittent elec-rical  discharges
IPC: B23H1/02
Filed: 1973-05-30
Abstract: 1432045 Electro-erosion ATELIERS DES CHARMILLES SA 30 May 1973 [16 June 1972] 25769/73 Heading B3V [Also in Divisions G3 and H3] An electro-erosion pulse generating circuit comprises a tool electrode 1, a workpiece electrode 2, a first switch S 1  connected between a D.C. source B 1  and a magnetic energy storage device L 1  for maintaining the current range in the storage device L 1  with a predetermined range, a first unidirectional conducting element D 1  connected between the storage device L 1  and the D.C. source B 1  for enabling the passage of current in a first auxiliary circuit when the switch S 1  is open, a second unidirectional conducting element D 2  connected between the D.C. source B 1  and one of the electrodes 1, 2 and a second switch S 2  for controlling the duration of the discharges and for enabling the passage of current into second and third auxiliary circuits. In the embodiment shown, the switch S 2  is controlled by a pulse generator 4 and the switch S 1  is controlled in accordance with the current through an induction coil L 1  by means of a device 3 which measures the current across a resistance R 1 . When both switches S 1 , S 2  are conductive, machining current is provided by the source B 1  through a lower voltage source B 2 , switch S 1  and induction coil L 1 . When the switch S 2  is opened to terminate the erosion discharge the current in the coil L 1  increases by passing through the diode D 2 , source B 2 , switch S 1  and resistance R 1 . When the current is greater than a first predetermined value, the switch S 1  is cut off by the device 3. With the switch S1 open and the switch S 2  closed, the current in the coil L 1  decreases by passing through the machining gap 1-2, switch S 2 , diode D 1 , and resistance R 1 . The switch S 1  is closed when the current in the coil L 1  is below a second, lower predetermined value. If both switches S 1 , S 2  are open, the current in the coil L 1  decreases in passing through the diode D 2 , source B 1 , diode D 1 , and resistance R 1 . Two power sources B 1 , B 3  may be used (Fig. 7, not shown) and source B 2  may be connected in series with the coil L 1  or diode D 2 . The coil L 1  may be connected to a transformer. In another embodiment (Fig. 4, not shown) the source B 2  is eliminated and the switch S 2  connected across the machining gap. The switch (S 3 ) (Fig. 5, not shown) for controlling the discharges may be connected across the coil L 1  and in series with a diode (D 3 ). Simultaneous closing of the switch S 1 , (S 3 ) is prevented by an inverter 6 and an AND gate 7. In another embodiment (Fig. 6, not shown) the source B 1  is connected to the maching gap through two switches (S 4 , S 5 ) and the coil L 1  is connected across the gap. The pulse generator 4 may be controlled by the discharge current which is passed through a resistance (R 2 ) (Fig 8, not shown) the voltage across which is applied to a trigger (8) for supplying a pulse to flip-flops (9, 10) the latter actuating the switch S 2  in the form of a transistor T 2 .